His Holiness is a style and form of address (in the variant form Your Holiness) for supreme religious leaders, most notably the Pope.
His Holiness (Latin: Sanctitas) is the official style used to address the Roman Catholic Pope and the Greek Orthodox Ecumenical Patriarch of Constantinople, as head of the Orthodox community. In February 2013, the Holy See announced that former Pope Benedict XVI would retain the style "His Holiness" after resigning and becoming Pope Emeritus.
The term is sometimes abbreviated or "HH" or "H.H." when confusion with "His/Her Highness" is unlikely. The associated form of address is "Your Holiness".
It is also used for certain other Eastern Patriarchs, notably those who head a church or rite whch recognizes neither Rome's nor Constantinople's primacy, notably any Catholicos of the East.
The English language honorific "His Holiness", and as female version "Her Holiness", has commonly been used for religious leaders from other traditions, including Buddhism (notably for the Dalai Lama), Shinto and in Ahmadiyya Islam for the Caliph.